Filling contact holes, trench lines, and other features with various materials is an integral part of semiconductor fabrication processes. For example, to form horizontal interconnects, vias between adjacent metal layers, contacts between first metal layers and devices, metals such as tungsten may be deposited using chemical vapor deposition (CVD) techniques. In a conventional deposition process, a substrate is heated to a predetermined process temperature in a deposition chamber, and a thin layer of tungsten-containing materials that serves as a seed or nucleation layer is deposited. Thereafter, the remainder of the tungsten-containing material (the bulk layer) is deposited on the nucleation layer. Conventionally, the tungsten-containing materials are formed by the reduction of tungsten hexafluoride (WF6) with hydrogen (H2). Tungsten-containing materials are deposited over an entire exposed surface area of the substrate including features and a field region.
Depositing materials into small and high aspect ratio features may cause formation of voids and seams inside the filled features. Large seams may lead to high resistance, contamination, loss of filled materials, and otherwise degrade performance of integrated circuits. For example, a seam may extend close to the field region after filling process and then open during chemical-mechanical planarization. Similarly, a void may cause problems with integration and performance.